A ventricular assist device (“VAD”is used to help supplement the heart's pumping action both during and after certain kinds of surgery, in situations where a complete cardiopulmonary bypass (using a heart-lung machine) is neither needed nor advisable in light of the serious side effects associated therewith. Ventricular assist devices typically comprise a pair of cannulae or other tubing and some sort of pump operably connected to the cannulae. In use, the cannulae are attached to either the left side of the heart (i.e., a left ventricular assist device, LVAD) or to the right side of the heart (i.e., a right ventricular assist device, RVAD) “in parallel” (i.e., the pump supplements the heart's pumping action but does not completely bypass it, and the pump is activated). Alternatively, a pump may be directly implanted into the body.
Originally, ventricular assist devices were air powered, wherein fluctuating air pressure, provided by a simple mechanical air pump machine, was applied to a bladder-like sac. The bladder had input and output valves, so that blood would enter the bladder through the input valve when the pressure on the bladder was low, and exit the bladder through the output valve when the pressure on the bladder was high. Unfortunately, these pneumatic ventricular assist devices were complicated, and used expensive mechanical valves that were prone to failure, subject to “clogging,” and that caused blood trauma or damage because of hard, metal edges and the like.
To overcome these problems, other types of ventricular assist devices were developed, including axial flow pumps for temporary insertion directly into the heart, and centrifugal pumps. The former are based on the Archymides' Principle, where a rod with helical blades is rotated inside a tube to displace liquid. In use, a catheter-mounted, miniature axial flow pump is appropriately positioned inside the heart, and is caused to operate via some sort of external magnetic drive or other appropriate mechanism. With high enough RPM's, a significant amount of blood can be pumped. In the case of centrifugal pumps, blood is moved by the action of a rapidly rotating impeller (spinning cone or the like), which causes the blood to accelerate out an exit. Both of these categories of ventricular assist devices are generally reliable and implantable, but are very expensive, not particularly durable, and are not useful in situations where a patient needs a true pulsating blood supply. Specifically, axial and centrifugal pumps are typically left on in a continuous operation mode, where a steady stream of blood is supplied on a continuous basis, as opposed to the natural rhythm of the heart, which acts on a periodic, pulse-producing basis. In addition, such pumps are still largely in the developmental or trial phase.
Accordingly, a primary object of the present invention is to provide a simpler pneumatic ventricular assist device that offers the advantages of pneumatic operation without the drawbacks associated with prior pneumatic devices.